1. Field of the Invention
The present invention relates to a method of manufacturing a bonded assembly, in particularly, a bonded assembly of glass, ceramics and a metal.
2. Description of the Related Art
Conventionally, as the art of bonding different kinds of material such as metal, ceramics and glass, there are known such methods as brazing, tin-alloy hard soldering, etc.
For bonding ceramics and metal by means of brazing, a material is required which is capable of bonding these. As such material, there is known active braze, i.e. Tixe2x80x94Agxe2x80x94Cu alloy, which can be wetted, in a molten state thereof, with ceramics.
For bonding between glass and metal, it has been conventional to employ a tin alloy with a component such as Zn having a high affinity relative to oxygen. In such case, the bonding is obtained by placing the tin alloy in its molten state with glass and metal with application of ultrasonic wave thereto.
An alternative method is known as metallizing method, according to which a metal layer is formed on the surface of ceramics and bonding is done with using a solder material made of metal.
With the above-described conventional methods, however, it has been difficult to bond plate-like bonding objects (i.e. objects to be bonded together) via only predetermined portions thereof with a predetermined constant gap and in a flawless condition. For instance, when an active braze is employed, it is needed to heat this solder material while applying a pressure to this material as being firmly held between the bonding objects. However, it has not been possible to always obtain an ideal condition in which the bonding portions are placed in gapless and tight contact with each other over the entire areas thereof. Further, with the bonding method using application of ultrasonic wave too, it has been difficult to form the bonding portions into a planar shape.
The present invention has been devised to overcome the above-described drawbacks of the conventional art. A primary object of the invention is to provide a method of bonding predetermined portions of objects efficiently and in a firmly contacted condition, in particular, such method allowing bonding flat plate-like objects without voids therebetween.
For accomplishing the above-noted object, the invention proposes a method of bonding respective objects made of different kinds of material to each other, the method comprises the steps of:
(A) contacting a bonding material in the fluid state thereof with respective bonding faces of the respective objects to be bonded;
(B) mechanically abrading portions of the respective bonding faces contacting the bonding material to be bonded to each other;
(C) setting the respective objects fixed in a predetermined position relative to each other while maintaining the respective objects in contact with the bonding material in the fluid state thereof; and
(D) solidifying the bonding material to bond the respective objects to each other;
characterized in that in the respective steps (A)-(D), the bonding material is present at the bonding portions to be bonded to each other of the respective objects constantly and without discontinuities.
In the above, what is referred to herein as xe2x80x9ca bonding material in the fluid state thereofxe2x80x9d represents e.g. a bonding material having such viscosity as allows the objects to be submerged therein, the viscosity being generally 104 Pa.s or less. Specific examples of the material includes resin, molten glass, molten salt, molten metal, etc. These materials which are fluidized by heating and are in the form of solids at the normal temperature can be used as the bonding material in the present invention.
Further, the step of xe2x80x9cmechanically abradingxe2x80x9d comprises activating means for forming bonding between the fluidized bonding material and the bonding surface portion of the object to be bonded. In particular, when the objects and the bonding material are of different kinds of material, because of the difference between the bonding structures of the materials, this activating means becomes essential. A typical example is a case when the bonding object is an oxide ceramics and the fluidized bonding material is a molten metal. Although the exact mechanism by which the mechanical abrasion promotes bonding between different kinds of materials is not known, it is believed that the energy by abrasion helps to break the energy barrier existing in the transformation of the bonding of the respective materials per se to the bonding between the materials.
Also, in the meaning of the present invention, the condition xe2x80x9cthe bonding material is present at the bonding portions of the respective objects constantly and without discontinuities.xe2x80x9d refers to the gaplessness or continuity in the bonding material in the course of movement thereof from the bonding portion of one object to the bonding portion of the other object. With this, when the objects are set at a predetermined position for allowing them to be finished as a bonded assembly, no voids are formed in the bonded portions thereof. If any void is present in the bonded portions, this result in disadvantageous reduction in the bonding strength and/or durability of the assembly. Therefore, this condition is important for obtaining a bonded assembly having a high bonding strength and durability.
When the bonding portions of the invention are to be used as air-tight sealing portions, the above condition is suitable as it assures voidless bonded condition.
That is, such condition of gap or void absent the bonding material being present between the bonding portions of different parts is out of the scope of the present invention. An example of this is a case when the bonding material is applied separately to each bonding portion and then these bonding portions are joined and bonded together. In such case, the object surface applied with the bonding material is inevitably exposed to the atmosphere in the course of the process to be rendered into a portion of a different property. More particularly, in case the bonding material is a molten metal, the exposure leads to generation of an oxide film thereon, and this film becoming the different-property portion. When the bonding faces are joined, such different-property portions tend to formation of voids, being not suitable as a bonded condition, even more unsuitable if they are used as air-tight sealing portions.
Preferably, the bonding material in the fluid state thereof comprises a molten metal, which includes a contact portion to be contacted to the atmosphere and a non-contact portion not to be contacted to the atmosphere, the non-contact portion of the molten metal being placed into contact with the contacting portions of the respective objects.
Metal material experiences elastic deformation and plastic deformation. Hence, it is possible to reduce stress generated in the bonding interface. So, metal material is advantageous with respect to the strength and durability of the bonding portions. On the other hand, with metal material, if exposed to oxygen-containing atmosphere in the molten state of the material, the material gradually experiences oxidation. In an inactive gas atmosphere or depressurized atmosphere, the progress of oxidation may be restricted to some extent. In practice, it is difficult to avoid oxidation for those metals having high affinty to oxygen, unless they are placed under a strongly reducing condition. It is desired for the purpose of obtaining greater strength and durability that the bonding portions be devoid of any oxides resulting from oxidation of molten metal employed as the bonding material. For this reason, it is preferred that in the bonding process, the molten metal to be placed into contact with the bonding portion of each object comprise the non-contact portion of the molten metal not exposed to the atmosphere, thus devoid of oxides.
Incidentally, a metal component having high affinity to oxygen can provide strong bonding in bonding to an oxide material in particular. Hence, it is preferred that the bonding material include such metal component. Moreover, in such case, if the metal material forming the bonding material contains oxygen, this sometimes can promote formation of bonding to the objects. For these reasons, it is preferred that the molten metal the molten metal employed as the bonding material be capable of taking in an appropriate amount of oxygen when exposed to the atmosphere and the non-contact portion of the molten metal not exposed to the atmosphere and devoid of oxides come into contact with the bonding portion.
Further, according to the present invention, preferably said steps (A)-(C) are effected at one time. An example of this is that the non-contact portion of the fluidized bonding material not exposed to the atmosphere is introduced to contact the bonding portions while the mechanical abrasion is applied to these portions simultaneously. With this, it is possible to manufacture a bonded assembly without any voids in an efficient manner.
Further and other features and advantages of the present invention will become apparent from the following detailed description with reference to the accompanying drawings.